1. Field of the Invention
The present invention relates to a tub for reserving washing water in a washing machine, and more particularly, to a tub that reduces noise generated during the operation of a drum-type washing machine in which the tub is arranged horizontally, and a method of manufacturing the tub.
2. Description of the Related Art
Generally, washing machines clean laundry by removing dirt from the laundry as the laundry rotates within a drum. Washing machines operate in a variety of methods. In recent years, a drum-type washing machine has been widely used. A drum-type washing machine includes a cabinet, a tub installed in the cabinet, and a drum rotatably installed in the tub.
The drum-type washing machines are classified into two types according to the power transmission method. That is, the first type is designed to transmit rotational force of a motor to the drum through a belt connecting a driving shaft of the motor to a central shaft of the drum. The second type is designed to directly transmit the driving force of the motor to the drum, in which the motor is directly mounted to the rear of the tub and a driving shaft of the motor is connected to a rear wall of the drum after passing through the tub. In the second type, the driving shaft of the motor transmits the rotational force of the motor to the drum through the driving shaft. Thus, vibration generated from the motor is transmitted together with the rotational force.
Vibration, including vibration generated from the motor and vibration generated while laundry is rotates within the drum, is then transmitted to the tub.
The vibration transmitted to the tub causes local resonance at various portions of the tub, which causes overall vibration of the tub. That is, portions of the tub amplify the vibration transmitted to the tub and cause the amount of noise produced by the tub to increase to an undesirable level.
Referring to FIG. 1, a vibration analysis was done using a related art tub and FIG. 1 visually depicts the vibration and noise produced by the tub. It can be clearly noted that each portion of the tub locally functions as a diaphragm when external vibration is applied to the tub. That is, when vibration having a predetermined frequency is applied to the tub, each portion of the tub amplifies the vibration thereby producing an undesirable amount of noise. This can be identified by the color changes of the local portions of the tub.
In order to solve the above problem in the related art, a sound insulation member encloses the outer circumference of the tub or the inner circumference of the cabinet disposed around the tub. However, the use of the sound insulation member increases the number of overall components in the washing machine. Furthermore, it is difficult to install the sound insulation member in the washing machine.
In addition, reinforcing ribs may be further installed on each portion of the tub where the vibration amplification may occur.
However, in order to form the reinforcing portion on each local portion, many mold pieces are required to manufacture the tub with the reinforcing ribs using plastic through an injection molding process. In this case, the size of the tub mold increases and a large capacity injection machine is required.
Therefore, the manufacturing cost increases, and thus it is difficult to actually employ this method.